Piezoelectric vibration piece and piezoelectric device

ABSTRACT

A piezoelectric vibration piece includes a base made of a piezoelectric material; a plurality of vibration arms which is integrally formed with the base and extends in parallel; elongate grooves which are formed along longitudinal directions of the vibration arms; and excitation electrodes which include inner electrodes disposed in the elongate grooves and side electrodes disposed in side surfaces facing the inner electrodes, wherein widening portions in which the widths of the vibration arms are widened toward the base at a joint between the vibration arms of the base are formed, and the side electrodes are led to principal surfaces and side surfaces of the widening portions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. Ser. No.11/387,101 filed Mar. 22, 2006 claiming priority to Japanese PatentApplication No. 2005-081501 filed Mar. 22, 2005, all of which areincorporated by reference herein.

BACKGROUND

1. Technical Field

The present invention relates to improvement of a piezoelectricvibration piece and a piezoelectric device which receives thepiezoelectric vibration piece in a package or a case.

2. Related Art

FIG. 7 is a schematic plan view illustrating an example of apiezoelectric vibration piece which has been conventionally used in apiezoelectric device and FIG. 8 is a schematic cross-sectional viewtaken along line A-A of FIG. 7.

In Figures, a piezoelectric vibration piece 1 is formed to have anillustrated outer shape by etching a piezoelectric material such asquartz and includes a rectangular base 2 and a pair of vibration arms 3and 4 which extends from the base 2 to a right side of FIG. 7. Elongategrooves 3 a and 4 a are formed in principal surfaces (front/rearsurfaces) of the vibration arms.

In other words, electrodes 5 and 6 applied with driving voltages to haveopposite polarities are provided in the base 2.

The electrode 5 is led to an inner surface of the elongate groove 3 aprovided in the vibration arm 3 and a side surface 4 b facing an innersurface of the elongate groove 4 a of the vibration arm 4.

The electrode 6 is led to the inner surface of the elongate groove 4 aprovided in the vibration arm 4 through a side electrode 6 a provided ina side surface 3 b facing the inner surface of the elongate groove 3 aof the vibration arm 3 and a base electrode 6 b provided in a principalsurface of the base 2 such that the electrode 6 is not short-circuitedto the electrode 5.

In addition, since an electrode must not be provided in a crotch portion2 a between the vibration arms 3 and 4, leading the side electrode 6 ato the base electrode 6 b is accomplished by forming an electrode 6 cconnected to the side electrode 6 a on the principal surface (front/rearsurface) of a sidewall 3 c of the vibration arm 3 and connecting theelectrode 6 c to the base electrode 6 b.

An electric field can be generated between the electrodes provided inthe inner surfaces of the elongate grooves 3 a and 4 a and theelectrodes provided in the side surfaces 3 b and 4 b of the vibrationarms 3 and 4 to reduce a crystal impedance value (hereinafter, referredto as “CI value”). Thus, it is possible to miniaturize the piezoelectricvibration piece.

However, in the miniaturized piezoelectric vibration piece, theabove-mentioned leading of the electrodes is not facilitated. Inparticular, since the width W1 of the sidewall 3 c of the vibration arm3 is very small, it is difficult to form the electrode 6 c on theprincipal surface of the sidewall 3 c, without coming into contact withthe electrode provided in the inner surface of the elongate groove 3 a.

Accordingly, a piezoelectric vibration piece 10 illustrated in FIG. 9which is a partial enlarged view illustrating the periphery of a root ofa vibration arm was suggested (for example, JP-A-2002-76827).

In the piezoelectric vibration piece 10, since the width W2 of anelongate groove 13 located at a joint of a vibration arm 14 is less thanthe width W3 of the front end of the elongate groove 13, it is possibleto surely form an electrode 12 on a sidewall without coming into contactwith an electrode provided in the inner surface of the elongate groove13 by the smaller width.

However, since a recent piezoelectric vibration piece has been newlyminiaturized, it is difficult to accurately form an electrode on aprincipal surface of a sidewall having a very small width in a vibrationarm. For example, since the width of the electrode 6 c of the principalsurface of the sidewall 3 c illustrated in FIG. 7 is at most 3 μm, theelectrode 6 c may not be formed on the principal surface of the sidewall3 c and thus the electrode 6 c and the electrode 6 b on the base 2 maynot be connected to each other. Although the electrode 6 c can beaccurately formed on the principal surface of the sidewall 3 c, theelectrode 6 c on the principal surface of the sidewall and the electrode6 b on the base 2 may be disconnected from each other due to slightdeviation of a position of the electrode 6 b on the base 2 connected tothe electrode 6 c.

In addition, according to the recent miniaturization of thepiezoelectric vibration piece, disconnection may occur even in thepiezoelectric vibration piece 10 illustrated in FIG. 9. For example, aposition of the electrode 12 on the principal surface of the sidewall isdeviated from a position 12 a indicated by a dotted line of FIG. 9 andthus the electrode 12 on the principal surface of the sidewall may bedisconnected from the side electrode 11.

Moreover, although the position of the electrode 12 on the principalsurface of the sidewall is slightly deviated, the disconnection betweenthe side electrode 11 and the electrode 12 on the sidewall can be avoidby more decreasing the width W2 of the elongate groove 13 illustrated inFIG. 9 and more increasing the width of the electrode 12 on theprincipal surface of the sidewall. However, when the width W2 of theelongate groove 12 is too small, the CI value increases.

SUMMARY

Accordingly, it is an advantage of the present invention to provide apiezoelectric vibration piece and a piezoelectric device using thepiezoelectric vibration piece, which can prevent electrodes from beingdisconnected from each other while preventing the electrodes from beingshort-circuited and can suppress a CI value to a low value, although thepiezoelectric vibration piece is miniaturized.

According to a first aspect of the invention, there is provided apiezoelectric vibration piece including a base made of a piezoelectricmaterial; a plurality of vibration arms which is integrally formed withthe base and extends in parallel; elongate grooves which are formedalong longitudinal directions of the vibration arms; and excitationelectrodes which include inner electrodes disposed in the elongategrooves and side electrodes disposed in side surfaces facing the innerelectrodes, wherein widening portions in which the widths of thevibration arms are widened toward the base at a joint between thevibration arms of the base are formed, and the side electrodes are ledto principal surfaces and side surfaces of the widening portions.

According to the first aspect, since the widening portion in which thewidths of the vibration arms are widened toward the base at the jointbetween the vibration arms of the base are formed, when the vibrationarms are bent and vibrated, largest stress is applied and rigidity ofthe joint in which distortion increases can be improved. Accordingly,the bending vibration of the vibration arms becomes stable and avibration component in an unnecessary direction is suppressed, therebysuppressing a CI value to a low value.

In addition, the side electrodes are led to the principal sides and theside surfaces of the widening portions. Accordingly, although theelectrode on the principal surface of the sidewall of the vibration armand the electrode on the base do not come into contact with each other,the side electrode and the electrode on the base can be connected toeach other through the electrode led to the principal surfaces and theside surfaces of the widening portions.

Moreover, since the side electrode and the electrode on the base can beconnected to each other without paying attention to the width of theelectrode of the principal surface of the sidewall of the vibration arm,the width of the electrode of the principal surface of the sidewall ofthe vibration arm may be decreased or the electrode of the principalsurface of the sidewall of the vibration arm may not be formed.Accordingly, it is possible to prevent the electrode of the principalsurface of the sidewall of the vibration arm from coming into contactwith inner electrode in the elongate groove.

Accordingly, even when the piezoelectric vibration piece isminiaturized, it is possible to provide a piezoelectric vibration piecewhich can prevent disconnection between electrodes while preventingshort-circuiting between the electrodes and can suppress the CI value toa low value.

According to a second aspect of the invention, the widths of thewidening portions may be widened toward the base while a widening degreestep is changed by step.

According to the second aspect, since the widths of the wideningportions is widened toward the base while a widening degree step ischanged by step, the contact length between the side surface of thewidening portion and the principal surface of the widening portion moreincreases, compared with a case where the widening degree is notchanged. Accordingly, it is possible to prevent the disconnectionbetween the side surface of the widening portion and the principalsurface of the widening portion.

According to a third aspect of the invention, there is provided apiezoelectric device which receives a piezoelectric vibration piece in apackage or a case, the piezoelectric vibration piece including a basemade of a piezoelectric material; a plurality of vibration arms which isintegrally formed with the base and extends in parallel; elongategrooves which are formed along longitudinal directions of the vibrationarms; and excitation electrodes which include inner electrodes disposedin the elongate grooves and side electrodes disposed in side surfacesfacing the inner electrodes, wherein widening portions in which thewidths of the vibration arms are widened toward the base at a jointbetween the vibration arms of the base are formed, and the sideelectrodes are led to principal surfaces and side surfaces of thewidening portions.

According to the third aspect, it is possible to a piezoelectric devicewhich can prevent electrodes from being disconnected from each otherwhile preventing the electrodes from being short-circuited and cansuppress a CI value to a low value.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a schematic plan view illustrating a piezoelectric deviceaccording to an embodiment of the invention.

FIG. 2 is a schematic cross-sectional view taken along line B-B of FIG.1.

FIG. 3 is a schematic perspective view illustrating a piezoelectricvibration piece used in the piezoelectric device of FIG. 1.

FIG. 4 is a cross-sectional view taken along line C-C of FIG. 3.

FIG. 5 is a partial view illustrating the periphery of a root of avibration arm of the piezoelectric vibration piece according to theinvention.

FIG. 6 is a partial enlarged view illustrating the periphery of a jointbetween vibration arms of a piezoelectric vibration piece according to amodified example of the invention.

FIG. 7 is a schematic plan view illustrating an example of apiezoelectric vibration piece which has been conventionally used in apiezoelectric device.

FIG. 8 is a schematic cross-sectional view taken along line A-A of FIG.7.

FIG. 9 is a partial enlarged view illustrating the periphery of a rootof a vibration arm.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIGS. 1 to 4 illustrate a piezoelectric device according to anembodiment of the invention, wherein FIG. 1 is a schematic plan viewthereof, FIG. 2 is a schematic cross-sectional view taken along line B-Bof FIG. 1, FIG. 3 is a schematic perspective view illustrating apiezoelectric vibration piece used in the piezoelectric device of FIG.1, and FIG. 4 is a cross-sectional view taken along line C-C of FIG. 3.

In addition, in FIGS. 1 and 2, for purposes of understanding, excitationelectrodes are not illustrated. Furthermore, the parallel oblique linesof FIG. 3 illustrate an electrode, not a cross section.

In the drawings, a piezoelectric device 30 illustrates an exampleconfiguring a piezoelectric vibrator. The piezoelectric device 30receives a piezoelectric vibration piece 32 in a package 37, asillustrated in FIGS. 1 and 2. The package 37 is formed by laminating afirst substrate 55 and a second substrate 56, as illustrated in FIG. 2,and is, for example, formed by molding and sintering a ceramic greensheet made of aluminum oxide in an illustrated shape using an insulatingmaterial.

In the package 37, an inner space S is formed by removing an innermaterial of the second substrate 56, as illustrated in FIG. 2. The innerspace S receives a piezoelectric vibration piece 32. In addition, onelectrode portions 31 and 31 formed on the first substrate 55, leadelectrodes 52 and 53 provided on a base 51 of the piezoelectricvibration piece 32 are bonded using conductive adhesives 43 and 43.Furthermore, the electrode portions 31 and 31 are connected to mountingterminals 41 and 42 on a rear surface of the package through conductivethrough-holes.

Moreover, after the piezoelectric vibration piece 32 is received, thepackage 37 is hermetically sealed by bonding a cover 40 made oftransparent glass using a sealing material 38. Accordingly, aftersealing the cover 40, laser light LB is irradiated to trim theelectrodes of the piezoelectric vibration piece 32, thereby performingfrequency regulation.

The piezoelectric vibration piece 32 is made of a piezoelectric materialsuch as quartz, lithium tantalate, or lithium niobium acid. Asillustrated in FIG. 3, the piezoelectric vibration piece 32 includes abase 51 and a pair of vibration arms 35 and 36 which bisects and extendsfrom the base 51 to an upper side of FIG. 3 in parallel.

In addition, a tuning-fork outer shape of the piezoelectric vibrationpiece 32 and elongate grooves provided in the vibration arms can beformed by wet-etching a material such as a quartz wafer using fluoricacid solution and dry-etching the material such as the quartz wafer.

The base 51 supports the vibration arms 35 and 36 and includes a regionfixed to the package 37 in the present embodiment.

In other words, the plurality of lead electrodes 52 and 53 connected tothe mounting terminals 41 and 42 (see FIG. 2) and having oppositepolarities are provided on the both ends of the base 51 in a widthdirection. The lead electrodes 52 and 53 deliver driving voltages to theexcitation electrodes and are formed by sputtering, for example, chrome(Cr) and gold (Au).

The vibration arm 35 and the vibration arm 36 have the substantiallysame outer shape, and elongate grooves 33 and 34 which extend on theprincipal surfaces (the front/rear surfaces) in a longitudinal directionare formed, respectively. Thus, as illustrated in FIG. 4, the crosssection of the vibration arms has substantially an H shape.

As illustrated in FIGS. 3 and 4, in the vibration arms 35 and 36, theexcitation electrodes, which are driving electrodes, are formed by innerelectrodes 44 and 45 disposed in inner surfaces of the elongate grooves33 and 34 and side electrodes 46 and 47 disposed in side surfaces 35 band 36 b facing the inner electrodes 44 and 45. In other words, theinner electrode 44 and the side electrode 46 face each other and theinner electrode 45 and the side electrode 47 face each other. The innerelectrodes 44 and 45 and the side electrodes 46 and 47 are connected tothe lead electrodes 52 and 53 on the base 51 to have oppositepolarities. The excitation electrodes are formed by sputtering, forexample, chrome (Cr) and gold (Au).

Accordingly, when the piezoelectric device 30 is mounted on a mountingsubstrate, an external driving voltage is delivered from the mountingterminals 41 and 42 to the respective excitation electrodes of thevibration arms 35 and 36 through the lead electrodes 52 and 53. At thistime, by applying driving voltages to the inner electrodes 44 and 45 andthe side electrodes 46 and 47 facing thereto, it is possible to improveelectric field efficiency in a region in which the excitation electrodesare formed in the elongate grooves 33 and 34 of the respective vibrationarms.

In addition, the inner electrodes 44 and 45 and the side electrode 46and 47 are preferably connected to the lead electrodes 52 and 53 to haveopposite polarities as follows.

First, the lead electrode 53 is connected to the inner electrode 44 ofthe elongate groove 33 through the principal surface (front/rearsurface) of the base 51 and to the side electrode 47 provided in theside surfaces 36 b facing the inner electrode 45 of the vibration arm36.

The lead electrode 52 is connected to the inner electrode 45 of thevibration arm 35 by rounding the front end and the side surface 35 b ofthe vibration arm 35 to be not connected to the lead electrode 53 andthe electrode of the principal surface of the base 51, the innerelectrode 44, and the side electrode 47 connected to the lead electrode53.

In other words, the lead electrode 52 is connected to the side electrode46 on the side surface 35 b of the vibration arm 35 and the sideelectrode 46 is connected to the inner electrode 45 in the elongategroove 34 of the vibration arm 35 through a connection electrode 48 ofthe principal surface (front/rear surface) of the base 51.

When the side electrode 46 is connected to the connection electrode 48of the base 51, the side electrode 46 is not covered by a crotch portion51 a located between the vibration arm 35 and the vibration arm 36 ofthe base 51 such that an electric field is not generated in the crotchportion 51 a.

Here, the piezoelectric vibration piece 32 according to the presentembodiment has widening portions 60 and 60 in which widths Wa of thevibration arms 35 and 36 are widened toward the base 51 at a jointbetween the vibration arms 35 and 36 of the base 51.

As illustrated in FIG. 1, the widening portions 60 and 60 are preferablyformed such that an outer widening portion 60 a and an inner wideningportion 60 b (at a side of the crotch portion 51 a) are symmetrical withrespect to an imaginary line CL along a longitudinal direction passingthrough a center of the vibration arms 35 and 36 in the width direction,when viewed in a plan view. Accordingly, the inner sides and the outersides of the vibration arms 35 and 36 are balanced and stable bendingvibration can be accomplished.

In particular, the widening portion 60 is inclined such that the widthof a root portion is inclined from the front end to the base 51 withoutchanging a widening degree when viewed in the plan view. As illustratedin FIG. 3, the side surface 60 c is inclined by a uniform angle.

In addition, the larger a maximum width Wb of a position contacting thebase 51, the easier the electrodes are led, as mentioned above.Accordingly, the widening portion 60 is widened to have a width greaterthan the width of the sidewall 35 a formed by providing at least theelongate groove 33. When the maximum width Wb of the widening portion 60is too large, the crotch portion 51 a is eliminated and thus thewidening portion 60 functions as the crotch portion. In order to avoidthe widening portion 60 from functioning as the crotch portion, thewidth of the crotch portion 51 a may increase, and, in this case, thewhole width of the piezoelectric vibration piece 32 increases.Accordingly, in order to leave the crotch portion 51 a, the wideningportion 60 is formed such that the maximum width Wb is about 23 μm. Inaddition, the length L1 of the widening portion 60 is 50 μm which is twotimes of the maximum width Wb.

Moreover, the side electrodes 46 and 47 are led to the side surfaces 60c, 60 c, 60 c, and 60 c of the widening portions 60, 60, 60, and 60.Furthermore, in the plurality of widening portions, the side electrode46 is led to the principal surface (front/rear surface) of the wideningportion 60 b in the vibration arm 35.

In other words, as mentioned above, the lead electrode 52 rounds theside surface and the front end of the vibration arm 35 to form the sideelectrode 46, and the side electrode 46 is led to the principal surfaceof the base 51 to form the connection electrode 48 connected to theinner electrode 45 of the vibration arm 36 on the base 51, such that thelead electrode 52 and the excitation electrode electrically connectedthereto, and the lead electrode 53 and the excitation electrodeelectrically connected thereto come into contact with each other.Accordingly, when the side electrode 46 is led to the connectionelectrode 48 on the base 51, the principal surface 60 d and the sidesurface 60 c of the widening portion 60 b are used.

The present embodiment of the invention is configured as mentionedabove, and the piezoelectric vibration piece 32 has the wideningportions 60 and 60 in which the widths Wa of the vibration arms 35 and36 are widened toward the base 51 at the joint between the vibrationarms 35 and 36 of the base 51. To this end, when the vibration arms 35and 36 are bent and vibrated, largest stress is applied and rigidity ofthe joint in which distortion is large can be improved. Accordingly, thebending vibration of the vibration arms 35 and 36 becomes stable and avibration component in an unnecessary direction (for example, athickness direction of the vibration arm) is suppressed, therebysuppressing the CI value to a low value.

In addition, the side electrode 46 is led to the principal surface 60 dand the side surface 60 c of the widening portion 60. Accordingly, asillustrated in FIG. 5 which is a partial view illustrating the peripheryof a root of the vibration arm 35, when the electrode of the principalsurface (front/rear surface) of the sidewall 35 a of the vibration arm35 is not accurately formed or when the electrode of the principalsurface of the sidewall 35 a is never formed, although the connectionelectrode 48 of the base 51 and the electrode of the principal surfaceof the sidewall 35 a of the vibration arm 35 do not come into contactwith each other, the side electrode 46 and the connection electrode 48on the base 51 are electrically connected to each other through theelectrode led to the principal surface 60 d and the side electrode 60 cof the widening portion 60, thereby avoiding the disconnection.

In addition, since the side electrode 46 and the connection electrode 48on the base 51 can be connected to each other without paying attentionto the electrode of the principal surface of the sidewall 35 a of thevibration arm 35, the width of the electrode of the principal surface ofthe sidewall 35 a of the vibration arm 35 may be decreased or theelectrode of the principal surface of the sidewall 35 a of the vibrationarm 35 may not be formed. Accordingly, it is possible to prevent theelectrode of the principal surface of the sidewall 35 a of the vibrationarm 35 from coming into contact with the inner electrode 44 in theelongate groove 33.

FIG. 6 is a partial enlarged view illustrating the periphery of a jointbetween vibration arms of a piezoelectric vibration piece according to amodified example of the invention.

In FIG. 6, the same reference numerals as those of the piezoelectricvibration piece 32 illustrated in FIGS. 1 to 5 are common elements andthus their description will be omitted. Hereinafter, portions differentfrom those of the piezoelectric vibration piece 32 illustrated in FIGS.1 to 5 will be described.

In FIG. 6, a piezoelectric vibration piece 70 is different from thepiezoelectric vibration piece 32 illustrated in FIGS. 1 to 5 in theshape of the widening portions 60.

In other words, in the piezoelectric vibration piece 70 illustrated inFIG. 6, the widths of the widening portions 60, 60, 60, and 60 arewidened toward the base 51 while a widening degree is changed step bystep. In other words, each widening portion 60 is formed to have achange point P for changing an angle when viewed in a plan view.

More preferably, in each widening portion 60, the widening degree of awidening portion 60-2 at the base side is greater than that of awidening portion 60-1 at the front end side. Accordingly, larger stressis applied and rigidity of the joint of the base side in whichdistortion increases can increase.

In addition, although, in the modified example of FIG. 6, the wideningdegree of each widening portion 60 is changed by one step and thewidening portions 60-1 and 60-2 having two different angles are formedwhen viewed in the plan view, the widening degree may be changed by atleast two steps.

The modified example of the invention is configured as mentioned aboveand the width of the widening portion 60 is widened toward the base 51while the widening degree is changed step by step, the contact lengthbetween the side surface 60 c of the widening portion 60 and theprincipal surface 60 d of the widening portion 60 can more increase,compared with a case where the widening degree is not changed.Accordingly, it is possible to more easily prevent disconnection betweenthe side surface 60 c of the widening portion 60 and the principalsurface 60 d of the widening portion 60, compared with the piezoelectricvibration piece 32 illustrated in FIGS. 1 to 5.

The invention is not limited to the above-mentioned embodiments. Theconfigurations of the embodiments may be combined to each other oromitted and may be combined with another configuration.

For example, the piezoelectric vibration piece 70 illustrated in FIG. 6may be received in the package 37 illustrated in FIGS. 1 and 2 to form apiezoelectric device. In addition, the package is not limited to abox-shaped package and may be, for example, a cylindrical container.

Moreover, even in the piezoelectric vibration piece, although the base51 is bonded to the package 37 in FIGS. 1 to 6, the invention is notlimited to this. For example, unlike the vibration arms 35 and 36, asecond arm portion may extend from an end of the base 51 and be bondedto the package.

The entire disclosure of Japanese Patent Application No. 2005-81501,filed Mar. 22, 2005 is expressly incorporated by reference herein.

1. A piezoelectric vibration piece comprising: a base made of apiezoelectric material; a plurality of vibration arms which isintegrally formed with the base and extends in parallel; elongategrooves which are formed along longitudinal directions of the vibrationarms; and excitation electrodes which include inner electrodes disposedin the elongate grooves and side electrodes disposed in side surfacesfacing the inner electrodes, wherein widening portions in which thewidths of the vibration arms are widened toward the base at a jointbetween the vibration arms of the base are formed, and the sideelectrodes are led to principal surfaces and side surfaces of thewidening portions.
 2. The piezoelectric vibration piece according toclaim 1, wherein the widths of the widening portions are widened towardthe base while a widening degree step is changed by step.
 3. Apiezoelectric device which receives a piezoelectric vibration piece in apackage or a case, the piezoelectric vibration piece comprises: a basemade of a piezoelectric material; a plurality of vibration arms which isintegrally formed with the base and extends in parallel; elongategrooves which are formed along longitudinal directions of the vibrationarms; and excitation electrodes which include inner electrodes disposedin the elongate grooves and side electrodes disposed in side surfacesfacing the inner electrodes, wherein widening portions in which thewidths of the vibration arms are widened toward the base at a jointbetween the vibration arms of the base are formed, and side electrodesare led to principal surfaces and side surfaces of the wideningportions.